In the art of cushion structures which are used in household furniture, beds and the like, foamed polyurethane mat, non-elastomeric, crimped polyester staple fiberfill, resin bonded fiber mat or thermally bonded fiber mat formed by adhering crimped polyester staple fibers, etc. have been used.
However, foamed polyurethane mat has problems that the chemicals used in the process of its production are difficult to handle and that freon is discharged. Furthermore, because the compression characteristics of foamed polyurethane mat show a unique feature that it is hard at the initial stage of compression and then abruptly sinks down, it not only is scanty in cushioning property but also gives a strong "bottom-hit feel". Still more, the mat has little air-permeability and consequently is apt to become stuffy, which renders the mat objectionable as a cushion structure in many cases. On top of it, foamed polyurethane mat is soft and has little resilient power to compression because it is foamed. The resilient power can be improved by increasing density of the foamed mat, but such also increases the weight and invites a fatal defect that its air-permeability is still aggravated. Further, non-elastomeric polyester staple fiberfill has defects that it is apt to be deformed during the use because the aggregate structure is not fixed, and its bulkiness or resilient power is considerably reduced as the constituent staple fibers migrate or the crimps therein fade away.
On the other hand, resin bonded fiber mat and thermally bonded fiber mat wherein non-elastomeric, crimped polyester staple aggregates are bound with a resin (e.g., polyacrylate) or binder fibers made of a polymer having a melting point lower than that of the polymer constituting the matrix staple fibers (Japanese Laid-Open Patent Application No. 31150/1983) show weak bonding strength. Also because the polymer film has a low elongation and little recovery from extension, the bonded points show low durability. Hence, such fiber mat products are apt to be broken when the bonded points are deformed during the use, or show poor recovery after deformation and consequently, their shape retention or resilient power drop drastically. Still more, since the bonded points are formed of a polymer of low elongation, they are rigid and lack mobility, resulting in poor cushioning performance. As means to improve the cushioning performance, Japanese Laid-Open Patent Application No. 102712/1087 proposes a cushion structure wherein the crossing points of crimped polyester staple fibers are fixed with a foamed polyurethane binder. The product, however, is apt to cause unevenness in processing because a solution type, crosslinkable polyurethane is impregnated. Consequently the treating solution is cumbersome to handle; adherability between polyurethane and polyester fibers is low; and because the binder is crosslinked, the product shows reduced elongation. Furthermore, because the resin portion is foamed, deformation tends to occur concentratively at localized spots. This leads to problems that it is easily broken when the foamed polyurethane at the fiber-crossing portions is heavily deformed; and that its durability is low.